Field of the Invention
The present invention relates to an image reading apparatus equipped with a reading position-determining unit that determines a reading position for an original.
Description of the Related Art
Conventionally, an image reading apparatus is known which performs reading of an original in a moving original reading mode, more specifically, conveys originals placed on a document tray using an automatic document feeder (ADF) one by one, and reads an image from each original by irradiating the original at a reading position with light emitted from a light source, and causing reflected light from the original to enter an image pickup device, such as a CCD sensor.
In an image reading apparatus equipped with the ADF, dust sometimes adheres to a portion of the original platen glass at the reading position due to paper dust of a conveyed original itself or a toner flake coming off toner printed on the original. Assuming that an original is read in the moving original reading mode in a state in which dust, such as paper dust or toner flake, adheres to the original platen glass, light emitted toward a surface of the original is blocked by the dust, which causes a vertical stripe to be formed in a read image at a position corresponding to a position of the original platen glass where the dust adheres. Therefore, in the image reading apparatus that reads an image from an original while conveying the original, it is desirable to determine a position on the original platen glass, where no dust adheres, as the original reading position, and then perform reading of the original.
As the image reading apparatus equipped with the reading position-determining unit, there has been proposed a technique in which the presence or absence of dust on an image read at a predetermined reading position is detected in a reading position setting mode, and when it is determined that dust is present, the reading position is changed to thereby detect the presence or absence of dust again (see Japanese Patent Laid-Open Publication No. 2004-179818 and U.S. Pat. No. 6,563,938). Then, if it is determined form the image read at the changed reading position that no dust is present, reading of an image from an original is performed at the changed reading position.
However, the above-described conventional technique is configured to determine a position on the original platen glass, where no dust adheres, as the reading position, and hence in a case where dust is present at each of a plurality of possible reading positions, it can occur that it is impossible to perform reading of an image.